Steric-influenced fluxionality in monomeric two and three coordinate copper(I) complexes with a trans-chelating bis-pyrazole ligand

Article abstract of DOI:10.1016/j.poly.2012.02.012

Two new trans-chelating bispyrazolyl ligands, L^H, where L ^H = 1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H- perimidine, and LCHPh₂, where LCHPh₂=2-benzhydryl-1,3-bis- (3,5-dimethyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H-perimidine, and their two and three coordinate copper(I) derivatives [Cu(L^H)](ClO₄) (3·ClO₄), [Cu(LCHPh₂)](ClO₄) (4·ClO₄), and [Cu(L^H)I] (5) were prepared and structurally characterized by X-ray crystallography. The variable-temperature ¹H NMR spectra showed that complex 4·ClO₄ is rigid, whereas complexes 3·ClO₄ and 5 are nonrigid in CH ₂Cl₂ solution. This suggests that the steric bulk of the 2-substituents in the dihydroperimidine moiety could impart some steric effects upon the fluxional behavior of individual two and three coordinate copper(I)-pyrazole complexes, in comparison with the rigid three coordinate copper(I) complex [Cu(L^Ph)I] (2) and dynamic two coordinate copper(I) complex [Cu(L^Ph)](ClO₄) (1·ClO₄) found previously [17]. To the best of our knowledge, complex 5 represents the first example of a dynamic monomeric three coordinate copper(I) complex.

Full text of DOI:10.1016/j.poly.2012.02.012

Polyhedron 37 (2012) 60–65
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Steric-influenced fluxionality in monomeric two and three coordinate copper(I)
complexes with a trans-chelating bis-pyrazole ligand
a
a
a
b
Chang-Chuan Chou a, , Hsueh-Ju Liu , Lucas Hung-Chieh Chao , Hong-Bin Syu , Ting-Shen Kuo
⇑
a Center for General Education, Chang Gung University of Science and Technology, Tao-Yuan 333, Taiwan
b Instrumentation Center, Department of Chemistry, National Taiwan Normal University, Taipei 11650, Taiwan
a r t i c l e i n f o
a b s t r a c t
Two new trans-chelating bispyrazolyl ligands, LH, where LH = 1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-
Article history:
2,3-dihydro-1H-perimidine, and LCHPh
,
where LCHPh ¼ 2-benzhy dryl-1; 3-bis-ð3; 5-dimethyl -pyra
2
2
Received 24 December 2011
Accepted 8 February 2012
Available online 27 February 2012
zol-1-ylmethylÞ-2; 3-dihydro-1H-perimidine, and their two and three coordinate copper(I) derivatives
[Cu(LH)](ClO4) (3ꢀClO4), ½CuðLCHPh2 ÞꢁðClO4Þ (4ꢀClO4), and [Cu(LH)I] (5) were prepared and structurally charac-
terized by X-ray crystallography. The variable-temperature 1H NMR spectra showed that complex 4ꢀClO4 is
rigid, whereas complexes 3ꢀClO4 and 5 are nonrigid in CH2Cl2 solution. This suggests that the steric bulk of
the 2-substituents in the dihydroperimidine moiety could impart some steric effects upon the fluxional
behavior of individual two and three coordinate copper(I)–pyrazole complexes, in comparison with the
rigid three coordinate copper(I) complex [Cu(LPh)I] (2) and dynamic two coordinate copper(I) complex
[Cu(LPh)](ClO4) (1ꢀClO4) found previously [17]. To the best of our knowledge, complex 5 represents the first
example of a dynamic monomeric three coordinate copper(I) complex.
Keywords:
Copper(I)
Two coordinate
Three coordinate
Fluxionality
Steric effect
Trans-chelating ligand
Ó 2012 Elsevier Ltd. All rights reserved.
2
1. Introduction
methyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H-perimidine (LCHPh ),
and their two and three coordinate copper(I) derivatives, [Cu(LH)]
H
2
Coordinatively unsaturated copper(I) complexes are useful
starting materials for the synthesis of copper(I) complexes having
small molecules (CO, NO, olefins, etc.) [1–7], and are particularly
valuable in bioinorganic modeling studies of Cu(I)/O2 chemistry
[8–14]. The synthesis and characterization of these sorts of
copper(I) complexes has, therefore, drawn considerable attention.
However, very few examples of dynamic two or three coordinate
copper(I) complexes have been reported [15–17]. As part of our
ongoing efforts to develop low-coordinate copper(I)–pyrazole
(ClO4) (3ꢀClO4), ½CuðLCHPh ÞꢁðClO4Þ (4ꢀClO4), and [Cu(L )I] (5), were
synthesized and structurally characterized by X-ray diffraction
analysis. Interestingly, variable-temperature 1H NMR spectra re-
vealed that complex 4ꢀClO4 is rigid, whereas complexes 3ꢀClO4
and 5 are nonrigid, suggesting that the steric bulk of the 2-stubstit-
uents in the dihydroperimidine moiety may impart some steric ef-
fects upon the fluxional behavior in the individual two and three
coordinate copper(I) complexes, as shown in Scheme 1. To our
knowledge, complex 5 represents the first example of a dynamic
mononuclear three coordinate copper(I) complex.
complexes [1,16,17], a perimidine-based bis-pyrazole ligand LPh
,
where LPh = 1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)2-phenyl-
2,3-dihydro-1H-perimidine (Scheme 1), was exploited, which can
serve as an effective trans-chelator for the synthesis of an uncom-
monly dynamic linear two coordinate copper(I) complex
[Cu(LPh)](ClO4) (1ꢀClO4) and a rigid T-shaped three coordinate cop-
per(I) complex [Cu(LPh)I] (2) [17]. Notably, these two complexes
can result in an iodide-controlled reversible change in fluorescence
and fluxionality (Scheme 1). To know whether the steric bulk of
2-substituents in perimidine influences the fluxional behavior in
the individual two and three coordinate copper(I) derivatives,
two new ligands, 1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)2,3-
dihydro-1H-perimidine (LH) and 2-benzhydryl-1,3-bis-(3,5-di-
2. Experimental
2.1. General information and materials
All manipulations were carried out using standard Schlenk lines
or glove-box techniques under an atmosphere of dinitrogen.
Acetonitrile and dichloromethane were distilled from calcium
hydride before use. Diethyl ether was dried by distillation from
sodium benzophenone prior to use. All reagents were obtained
from commercial sources and used as received without further
purification. The starting material CuI is purchased and used as
received. The [Cu(MeCN)4](ClO4) was prepared according to
literature procedures [18]. Warning: Perchlorate compounds are
potentially explosive! Extreme care must be taken when working
⇑
Corresponding author. Tel.: +886 3 2118999x5583; fax: +886 3 2118866.
E-mail address: ccchou@mail.cgust.edu.tw (C.-C. Chou).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.012

C.-C. Chou et al. / Polyhedron 37 (2012) 60–65
61
+
direct methods and refined by full-matrix least-squares procedures
using the SHELXL-97 program [19]. All of the non-hydrogen atoms
were refined with anisotropic temperature factors. All hydrogen
atoms were located geometrically and refined in the riding mode.
R
_
R
I
N
N
N
N
N
N
H
N
N
H
Cu
2.4. Synthesis of LH
N
N
N
N
Cu
A mixture of 1,8-diaminonaphthalene (1.28 g, 8.1 mmol) and
3,5-dimethylpyrazolemethanol (3.08 g, 24.4 mmol) in 35 mL of
CH3CN was stirred in a closed round-bottomed flask at room tem-
perature for 48 h. The resulting light brown precipitate was filtered
and extracted from hot n-hexane to yield LH 2.29 g (73%). Colorless
needle crystals of LH were obtained after crystallization from n-
hexane. 1H NMR (CD2Cl2, 500.13 MHz): d 7.33–7.30 (m, 4H, CH of
naphthalene), 6.95–6.93 (m, 2H, CH of naphthalene), 5.82 (s, 2H,
CH of pyrazolyl), 5.41 (s, 4H, CH2), 4.50 (s, 2H, CH2 of perimidine),
2.19 (s, 6H, CH3), 2.17 (s, 6H, CH3) ppm. 13C NMR (CD2Cl2,
125.77 MHz): d 148.22 (CH of pyrazolyl), 142.23 (CH of pyrazolyl),
140.09 (C of naphthalene), 135.69 (C of naphthalene), 127.15 (C of
naphthalene), 119.88 (CH of naphthalene), 117.52 (CH of naphtha-
lene), 107.70 (CH of pyrazolyl or naphthalene), 106.55 (CH of naph-
thalene or pyrazolyl), 64.02 (CH2), 63.93 (CH2), 13.85 (CH3), 11.46
(CH3) ppm. Positive ESI-MS: 409.4 (M+Na+, 100%). mp = 164 °C.
Anal. Calc. for C23H26N6: C, 71.48; H, 6.78; N, 21.74. Found: C,
71.06; H, 6.64; N, 21.84%.
I
Fluxional for R = Ph (1+) and H (3+)
Rigid for R = CHPh2 (4+)
Rigid for R = Ph (2)
Fluxional for R = H (5)
Scheme 1. Structure and fluxionality of copper(I) complex cations 1, 3 and 4; and
Cu–I complexes 2 and 5.
with perchlorate complexes, and only small quantities should be
handled.
2.2. Physical measurements
Infrared spectra were recorded on a Bruker Alpha-T FTIR spec-
trometer as Nujol mulls. Variable-temperature 1H NMR spectra
were obtained on Bruker Avance 500.13 MHz NMR spectrometer
equipped by a temperature regulator. Data were recorded in CD2Cl2
at temperature ranging from 300 to 180 K. 13C NMR spectra were
recorded on Bruker Avance 125.77 MHz spectrometer. Mass spectra
were acquired on a Finnigan TSQ 700 spectrometer. Elemental anal-
yses were performed on a HERAEUS CHN–O–S-Rapid elemental
analyzer by Instruments Center, National Chung Hsin University,
and a HERAEUS VarioEL-III Analyzer by Advanced Instrument Cen-
ter, National Taiwan University. Fluorescence emission spectra
were recorded at ambient on a Hitachi F-7000 fluorescence spectro-
photometer. UV–Vis spectra were recorded on a Hewlett Packard
8453 Ultraviolet/Visible Absorption Spectrometer.
2.5. Synthesis of 2-benzhydryl-2,3-dihydro-1H-perimidine:
the precursor of LCHPh
2
A 20 mL absolute EtOH (99.5%) solution of 1,8-diaminonaphtha-
lene (1.58 g, 0.01 mol) and diphenylacetaldehyde (1.96 g, 0.01 mol)
was stirred at room temperature for 24 h. The white precipitates
formed were filtered and washed with hexane. The solid was puri-
fied on a silica chromatography column with CH2Cl2/hexane (1:1)
as eluent to give 2.58 g (77% yield) of white powder (Rf = 0.42). IR(-
Nujol): mN–H 3399, 3381 cmꢂ1. Positive ESI-MS: 337.5 [M++1]. 1H
NMR (CDCl3, 500.13 MHz): d 7.20–7.44 (m, 14H, CH of aromatic),
2.3. X-ray crystallography
Crystal data collection and processing parameters are given in
Table 1. Diffraction data were carried out on a Bruker Kappa CCD
diffractometer with graphite monochromated Mo K
(k = 0.7107 Å). The structures 3ꢀClO4, 4ꢀClO4 and 5 were solved by
3
6.37 (dd, 2H, CH of aromatic), 5.22 (d, 1H, CH, JH,H = 9.70 Hz),
3
4.42 (s, 2H, NH), 4.23 (d, 1H, CH, JH,H = 9.70 Hz) ppm. 13C NMR
a radiation
(CDCl3, 125.77 MHz): d 141.00, 139.64, 134.74, 129.19, 128.40,
127.45, 126.85, 117.47, 113.64, 105.77, 66.77, 56.75 ppm. Anal.
Calc. for C24H20N2: C, 85.68; H, 5.95; N, 8.33. Found: C, 86.05; H,
5.91; N, 8.67%.
Table 1
X-ray crystallographic data for complexes 3ꢀClO4–5.
3ꢀClO4
4ꢀClO4ꢀCH2Cl2
5
Formula
Formula weight
T (K)
C
23H26ClCuN6O4 C37H38Cl3CuN6O4 C23H26CuIN6
2.6. Synthesis of [Cu(LH)](ClO4) (3ꢀClO4)
549.49
296(2)
0.71073
monoclinic
P21/n
13.262(5)
13.460(5)
13.589(4)
90
96.36(2)
90
2410.7(14)
4
800.62
200(2)
576.94
200(2)
A
10 mL CH2Cl2 solution of [Cu(MeCN)4]ClO4 (153.2 mg,
k (Å)
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/n
0.47 mmol) and LH (181.2 mg, 0.47 mmol) was stirred at room
temperature for 1 h under N2. Then 15 mL Et2O was introduced
into the solution and a white precipitate formed. After filtering,
the product was washed by 5 mL CH2Cl2 and 10 mL Et2O for two
times and dried in vacuo to yield 213.4 mg (83%). The crystals suit-
Crystal system
Space group
a (Å)
b (Å)
c (Å)
14.1640(4)
15.9768(4)
16.1429(5)
90
12.5327(6)
13.7666(8)
13.3413(8)
90
a
(°)
b (°)
94.1730(10)
90
90.807(4)
90
able for X-ray structure determination were grown from CH2Cl2/
c
(°)
Et2O. IR(Nujol): mClO 1102, 621 cmꢂ1
.
1H NMR (CD2Cl2,
ꢂ
V (Å3)
3643.38(18)
4
2301.6(2)
4
4
500.13 MHz, 300 K): d 7.38–7.30 (m, 4H, H of naphthalene),
6.52–6.50 (m, 2H, H of naphthalene), 6.05 (s, 2H, CH of pyrazolyl),
5.74 (s, 4H, CH2), 5.58 (s, 2H, CH2), 2.54 (s, 6H, CH3), 2.32 (s, 6H,
CH3) ppm. 1H NMR (CD2Cl2, 500.13 MHz, 179.9 K): d 7.31–7.25
(m, 4H, naphthalene H), 6.41–6.40 (m, 2H, naphthalene H), 6.03
Z
Dcalc (Mg mꢂ3
)
1.514
1.060
17996
4244(0.0865)
1.460
1.665
l
(mmꢂ1
)
0.869
2.313
Collected reflections
Unique reflections
14921
10402
6406(0.0609)
4041(0.1095)
(Rint
)
(s, 2H, CH of pyrazolyl), 5.75 (d, 2H, methylene CH2–CHa,
Parameters
Reflections with
316
2417
460
280
2
4593
2157
2JH,H = 13.67 Hz), 5.58 (d, 2H, methylene CH2–CHb, JH,H
=
2
I > 2r(I)
13.67 Hz), 5.42 (d, 1H, perimidine CH2–CHa, JH,H = 10.63 Hz),
b
R1a, wR2
0.0541, 0.1165
0.0649, 0.1757
0.0742,
0.1605
2
4.84 (d, 1H, perimidine CH2–CHb, JH,H = 10.63 Hz), 2.50 (s, 6H,
CH3), 2.26 (s, 6H, CH3) ppm. 13C NMR (CD2Cl2, 125.77 MHz): d
151.82, 143.22, 139.96, 135.95, 127.16, 121.36, 117.88, 108.00,
106.98, 69.97, 64.22, 15.55, 12.01 ppm. Positive ESI-MS: 449.2
P
P
a
R1
=
(Fo ꢂ Fc)/ Fo.
P
P
2
2
1=2
b
wR2 ¼ f ½wðFo ꢂ FcÞ ꢁ= ½wðFoÞ ꢁg
.

62
C.-C. Chou et al. / Polyhedron 37 (2012) 60–65
(M+, 100%). Anal. Calc. for C23H26ClCuN6O4: C, 50.27; H, 4.74; N,
15.29. Found: C, 50.65; H, 4.98; N, 15.16%.
3,5-dimethylpyrazolemethanol in a molar ratio of 1:3, which gave
a six-membered C4N2 heterocyclic ring by N–C bond coupling,
accompanied by the loss of one molecule of 3,5-dimethylpyrazole
(EI/Mass e/m = 98 (24%)), as depicted in Scheme 2. The ligand LH
was fully characterized by 1H, 13C NMR and ESI-MS spectroscopy,
together with X-ray diffraction analysis.
Complexes 3ꢀClO4 and 4ꢀClO4 were synthesized from the reac-
tion of ligands LH and LCHPh2 , respectively, with [Cu(CH3CN)4](ClO4).
Complex 5 can be prepared from the treatment of 3ꢀClO4 with n-
Bu4NI in the CH2Cl2 or directly from the reaction of LH with CuI.
The elemental analyses and ESI-MS of 3ꢀClO4, 4ꢀClO4 and 5 were
in agreement with the proposed formulas. The variable-tempera-
ture 1H NMR spectra of 3ꢀClO4 and 5 confirmed the fluxional
behavior of these two complexes.
2.7. Synthesis of [Cu(LCHPh )] (4ꢀClO4)
2
A 30 mL CH3CN solution of 2-benzhydryl-2,3-dihydro-1H-per-
imidine (1.68 g, 5.0 mmol) and (3,5-dimethylpyrazol-1-yl)metha-
nol (1.26 g, 10.0 mmol) was stirred at room temperature for 72 h.
The solvent was removed in vacuo to afford an oily crude product
of LCHPh 2.76 g (5.0 mmol). IR(Nujol): mClO 1103, 621 cmꢂ1. Posi-
2
ꢂ
4
tive ESI-MS: 575.3 ([M+Na]+, 100%). The reaction of [Cu(MeCN)4]-
ClO4 (248.2 mg, 0.76 mmol) and the oily LCHPh (500.6 mg,
2
1.17 mmol) was then performed at room temperature for 1 h un-
der N2. After cooling the solution to 0–5 °C, 15 mL Et2O was intro-
duced to afford white powder of 4ꢀClO4. The resulting solid was
collected by filtration, washed with hexane and dried in vacuo to
yield 0.28 g (62%). The crystals suitable for X-ray structure deter-
mination were grown from CH2Cl2/Et2O. 1H NMR (CD2Cl2,
500.13 MHz,): d 7.28–7.43 (m, 14H, CH of aromatic), 6.52 (d, 1H,
3.2. X-ray structures of the complexes
The crystal structures of complex cations 3 and 4 are exhibited
in Figs. 1 and 2, respectively. The copper(I) ion is coordinated by
two pyrazole nitrogen atoms with the N(Pz0)–Cu–N(Pz0) bond an-
gles of 167.3(2)° toward N3 for 3+ and 167.9(1)° toward N4 for
4+, forming a 10-membered metallocycle. The dihedral angles of
the two pyrazoles are 9.5(2)° for 3+ and 14.4(2)° for 4+. Due to ring
strain, the Cu1. . .N(amine) contacts are restricted for these two
complexes. The contact of Cu1. . .N3 is 2.604(4) Å for 3+ and
2.731(3) Å for 4+, which leads to a N–Cu–N structure bent toward
N(amine) and displays weak coordination [20]. The Cu1–N(Pz0)
distances of 1.890(5) Å for 3+ and 4+ are similar to those previously
reported for two-coordinate copper(I)–pyrazole complexes: 1.87–
1.88 Å [21].
2
2
CH, JH,H = 10.55 Hz), 6.07 (d, 2H, CH of aromatic, JH,H = 7.40 Hz),
2
5.93 (s, 2H, CH of pyrazolyl), 5.45 (d, 2H, CH, JH,H = 13.75 Hz),
2
2
4.57 (d, 2H, CH, JH,H = 13.70 Hz), 4.35 (d, 1H, CH, JH,H = 10.60 Hz),
2.26 (s, 6H, CH3), 2.23 (s, 6H, CH3) ppm. 13C NMR (DMSO-d6,
125.77 MHz): d 149.65, 142.49, 139.07, 135.52, 134.45, 128.77,
128.52, 127.29, 127.23, 119.23, 115.79, 106.97, 105.69, 78.33,
61.78, 53.39, 14.40, 10.61 ppm. Positive ESI-MS: 615.3 ([MꢂClO4]+,
100%). UV–Vis (CH2Cl2) kmax, nm (e
, Mꢂ1 cmꢂ1): 346 (17262), 332
(15849). Anal. Calc. for C36H36CuN6ClO4: C, 60.42; H, 5.03; N,
11.75. Found: C, 60.55; H, 5.01; N, 11.53%.
2.8. Synthesis of [Cu(LH)I] (5)
The crystal structure of complex 5 (Fig. 3) is very similar to that
of complex 2 [17]. The N(Pz0)–Cu–N(Pz0) bond angle of 148.5(4)°
grossly deviates from linearity, and the dihedral angle of the coor-
dinated pyrazole rings is 18.2° for complex 5, which is an 8.7° lar-
ger than that of 3+ due to the coordination of iodide anion. The
bond angle around the copper center is 359.3°. Complex 5 has a
longer Cu1–N(Pz0) bond distances of 1.937(6) Å and a considerably
longer Cu1–I1 bond distance of 2.790(2) Å, which are characteristic
of three-coordinate T-shaped binding [21–27]. The grossly non-
equivalent contact of Cu1. . .N(amine), Cu1. . .N3 of 3.237(11) Å
and Cu1. . .N4 of 2.622(10) Å, remains in spite of coordination of
the iodide anion, which can be considered as a weak coordination
like complex cation 3.
The bond angles between the Cu1–N3(amine) bond and the
other bonds around the N3(amine) atom are larger than 90°, indi-
cating that the N3 atom is an sp3 tetrahedral hybridization, and the
lone pair of electrons are capable of pointing to the Cu1 center. On
the other hand, the sum of the bond angles around the N4(amine)
atom is 360°. Nonetheless, due to a very weak Cu1. . .N(amine)
The reaction of CuI (83.9 mg, 0.44 mmol) and LH (178.9 mg,
0.46 mmol) was carried out in 10 mL CH3CN under N2 for 1 h. After
filtering, the product was washed by 5 mL CH3CN and 10 mL Et2O
for two times and dried in vacuo to yield 149.0 (59%). X-ray-quality
crystals were grown by Et2O diffusion into saturated CH2Cl2 solu-
tion. 1H NMR (CD2Cl2, 500.13 MHz, 300 K): d 7.34–7.27 (m, 4H,
CH of naphthalene), 6.57–6.55 (d, 2H, CH of naphthalene), 5.96
(m, 2H, CH of pyrazolyl), 5.65 (s, 4H, CH2), 5.11 (s, 2H, CH2 of per-
imidine), 2.46 (s, 6H, CH3), 2.29 (s, 6H, CH3) ppm. 1H NMR (CD2Cl2,
500.13 MHz, 203.2 K): d 7.25–7.24 (m, 4H, naphthalene H), 6.45
(br, 2H, naphthalene H), 6.11–5.93 (br, 1H, perimidine CH2–CHa,
2H, methylene CH2–CHa, 2H, CH of pyrazolyl), 5.61 (d, 2H, methy-
2
lene CH2–CHb, JH,H = 12.65 Hz), 4.63 (d, 1H, perimidine CH2–CHb,
2JH,H = 8.40 Hz), 2.48 (s, 6H, CH3), 2.24 (s, 6H, CH3) ppm. 13C NMR
(CD2Cl2, 125.77 MHz, 300 K): d 149.54, 141.61, 141.30, 135.56,
127.03, 121.04, 118.06, 107.77, 107.22, 67.77, 64.14, 14.87,
11.96 ppm. Positive ESI-MS: 449.3 ([MꢂI]+, 100%). Anal. Calc. for
C23H26CuN6I: C, 47.88; H, 4.54; N, 14.57. Found: C, 47.44; H,
4.51; N, 14.41%.
2
N
N
3. Results and discussion
HO
RCHO
N
N
N
N
R
3.1. Preparation of the ligand and the complexes
In a preceding report we noted the synthesis of ligand LPh [17].
HN
NH
N
NH2 NH2
N
R
LR
( HOCH2Pz' )
The formation of ligand LCHPh can follow the same procedure, as
2
shown in Scheme 2. Though purification of the ligand LCHPh is dif-
2
3
HO
N
N
_
Pz'
HPz'
Pz'
ficult, further complexation with [Cu(CH3CN)4](ClO4) can give a
N
N
N
N
_
pure copper(I) derivative, ½CuðLPh CHÞꢁðClO4Þ (4ꢀClO4), with no diffi-
3 H2O
2
H
N
N
N
N
culty. An attempt to prepare ligand LH was unsuccessful by the
same synthetic route when diphenylacetaldehyde was replaced
by formaldehyde. However, a more direct approach was found by
the straightforward treatment of 1,8-diaminonaphthalene with
N
N
LH
Scheme 2. The formation of ligands LPh (R = Ph), LCHPh2 (R = CHPh2) and LH.

C.-C. Chou et al. / Polyhedron 37 (2012) 60–65
63
Fig. 3. ORTEP drawing of molecular structure of complex 5 with thermal ellipsoids
drawn at 30% probability level. Selected bond distances (Å) and bond angles (°):
Cu1–N1 1.942(10), Cu1–N6 1.931(10), Cu1...N3 3.237(11), Cu1...N4 2.622(10), Cu1–
I1 2.790(2), C7–N3 1.385(15), C6–N3 1.437(17), C17–N3 1.451(15), C13–N4
1.397(15), C17–N4 1.473(15), C18–N4 1.451(14); N1–Cu1–N6 148.5(4), N6–Cu1–
I1 109.0(3), N1–Cu1–I1 101.8(3), C6–N3–C7 121(1), C7–N3–C17 114(1), C6–N3–
C17 124(1), C13–N4–C17 112.0(9), C13–N4–C18 119(1), C17–N4–C18 115.6(9),
N3–C17–N4 110(1).
Fig. 1. ORTEP drawing of complex cations 3 with thermal ellipsoids drawn at 30%
probability level. Selected bond distances (Å) and bond angles (°): Cu1–N1 1.889(4),
Cu1–N6 1.886(4), Cu1...N3 2.604(4), Cu1...N4 3.113(4), C7–N3 1.406(5), C6–N3
1.440(6), C17–N3 1.455(6), C13–N4 1.392(6), C17–N4 1.438(6), C18–N4 1.429(6);
N1–Cu1–N6 167.3(2), C6–N3–C7 119.3(4), C7–N3–C17 113.5(3), C6–N3–C17
116.1(4), C13–N4–C17 116.0(4), C13–N4–C18 122.2(4), C17–N4–C18 121.8(4),
N3–C17–N4 108.6(4).
NMR spectra over the temperature range 180–300 K in CD2Cl2 is
considered to be a rapid conformational equilibration of the
framework in solution. It is likely that the exchange rate is too fast
to be observable. After coordinating to the copper(I) ion, the
bridging methylene H2C(7) and the other two methylenes
[H2C(6) + H2C(18)] of the ligand display broad peaks at 225 and
246 K (coalescence temperature) in CD2Cl2 for complexes 3ꢀClO4
and 5, respectively, indicating that the exchange rate of these
methylenes can be slowed by coordination.
In complex 3ꢀClO4, two kinds of dynamic methylenes H2C(17)
and [H2C(6) + H2C(18)] are observed, which further split into a
sharp doublet of doublets when the temperature is lowered to
180 K, while the other peaks remain unchanged (Fig. 4). This
behavior is justified by the diastereotopic nature of the methylene
groups H2C(6), H2C(17) and H2C(18) at low temperatures. Because
the coalescence temperature of these two kinds of methylene is
virtually the same in complexes 3ꢀClO4 (Tc = 246 K), a common
mechanism for these two kinds of methylenes in 3ꢀClO4 is
suggested. It is inferred that there could be at least four
Fig. 2. ORTEP drawing of complex cations 4 with thermal ellipsoids drawn at 30%
probability level. Selected bond distances (Å) and bond angles (°): Cu1–N1 1.891(3),
Cu1–N6 1.892(3), Cu1...N3 2.731(3), Cu1...N4 2.961(3), C7–N3 1.409(5), C6–N3
1.433(5), C17–N3 1.464(5), C13–N4 1.403(5), C17–N4 1.458(5), C18–N4 1.440(5);
N1–Cu1–N6 167.9(1), C6–N3–C7 121.1(3), C7–N3–C17 116.6(3), C6–N3–C17
117.5(3), C13–N4–C17 116.2(3), C13–N4–C18 122.9(3), C17–N4–C18 119.9(3),
N3–C17–N4 106.8(3).
N6
N6
N1
N1
Cu
Ha
Cu
Ha
N2
N2
N5
N5
Ha
He
Ha
He
Ha
He
Ha
He
N4
N3
N3
N4
He
He
interaction and an approximately symmetrical structure, the prob-
able p–electron delocalization in the perimidine nucleus may pro-
( D )
( B )
ceed to an exchange contact with Cu1. . .N3 M Cu1. . .N4 in
solution, as shown in Scheme 3, (A) M (C) or (B) M (D), which is
in agreement with the observed 1H NMR spectra in solution.
He
Ha
He
Ha
N3
Ha
He
Ha
He
Ha
He
Ha
He
N4
N4
N3
3.3. Spectroscopic features
N2
N5
N2
N5
3.3.1. Solution dynamics
Cu
Cu
( A)
N6
N1
For ligand LH, the 1H and 13C NMR spectra show only a single set
of peaks, indicating a symmetrical structure. The diastereotopic
nature of the bridging methylene and the other two methylenes
solely exhibiting a singlet peak in the variable-temperature 1H
N6
N1
( C )
Scheme 3. Projection of the proposed fluxional process of the 10-membered
metallocycle in complex cation 3.

64
C.-C. Chou et al. / Polyhedron 37 (2012) 60–65
conformations involved in equilibration, as depicted in Scheme 3,
to lead to an exchange of H(equatorial) M H(axial) in methylene
H2C(7) and [H2C(6) + H2C(18)]. For example, when the exchange
of Ha(axial) and He(equatorial) on C17 takes place, two pyrazolyl
groups must move to the opposite face of the naphthalene ring,
as shown in Scheme 3 conformer (A) M conformer (B) or con-
former (C) M conformer(D), suggesting the probable opening up
of the N(Pz0)–N(Pz0) chelate ring. The exchange of the diastereotop-
ic protons on C6 and C18 could accomplish this. Due to the very
weak Cu1. . .N(amine) interaction and the average symmetrical
structure, an exchange contact of Cu1. . .N3 M Cu1. . .N4 (Scheme
3, (A) M (C) or (B) M (D)) could possibly proceed in solution, which
is in agreement with the observed 1H NMR spectra. In complex 5,
dynamic behavior obviously took place, although the variable-tem-
perature 1H NMR spectra are somewhat broad for the resonance of
methylene H2C(17) and [H2C(6) + H2C(18)] (Fig. 5). The interchange
of methylene protons H2C(17) and [H2C(6) + H2C(18)] occurred at
the same Tc (225 K) as in complex 3ꢀClO4, suggesting a common
mechanism for these methylenes as well. The detailed mechanisms
for complexes 3ꢀClO4 and 5, are not fully understood, and remain to
be determined in the future.
Comparing the three coordinate Cu–I complexes 5 and 2, we can
see that the replacement of the bulky phenyl group with a hydro-
gen atom at C17 can result in the display of fluxional behavior.
However, for the two coordinate complex 1ꢀClO4, the phenyl group
at C17 does not appear to be bulky enough to hamper the dynamic
behavior. When a more sterically hindered substituent 2-benzhy-
dryl is replaced at the C17 position, the dynamic behavior
effectively ceases, as with complex 4ꢀClO4. Apparently the 2-sub-
stituents at C17 may impart some steric effects upon the dynamic
behavior of both two and three coordinate copper(I) complexes of
the presented ligand system.
3.3.2. Photophysical properties
The absorption spectra of ligand LH and complexes 3ꢀClO4 and 5
in CH2Cl2 are exhibited in (S3), and are assigned to a ligand-cen-
tered
perturbation of the
p–
p⁄ transition. A comparison of these spectra revealed the
p–
p⁄ transition of the perimidine fluorophore,
suggesting the existence of weak Cu1. . .N(amine) interactions. For
complex 3ꢀClO4, the blue shift profile is evident, whereas for com-
plex 5, the p–
p⁄ orbital perturbation occurs to a lesser extent be-
cause of the neutralization of the iodide anion. For complex 5, an
additional broad shoulder that appeared at 270 nm was assigned
as the copper(I)-to-pyrazole MLCT transition [17,28].
The emission profiles of LH and its copper(I) complexes are com-
pared and shown in Scheme 4. The fluorescent properties of LH and
its copper(I) complexes greatly resemble those of the LPh ligand
Fig. 4. Variable-temperature 1H NMR spectra of complex 3ꢀClO4 over the stated
Fig. 5. Variable-temperature 1H NMR spectra of complex 5 over the stated range of
temperatures.
range of temperatures.

C.-C. Chou et al. / Polyhedron 37 (2012) 60–65
65
acknowledged. We thank Miss C.-H. He for assistance with vari-
able-temperature NMR data.
80
60
40
20
0
Appendix A. Supplementary data
CCDC 782810, 857494 and 782809 contain the supplementary
crystallographic data for 3ꢀClO4, 4ꢀClO4, and 5. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version, at
doi:10.1016/j.poly.2012.02.012.
350
400
450
500
550
References
Wavelength (nm)
[1] C.-C. Chou, C.-C. Su, A. Yeh, Inorg. Chem. 44 (2005) 6122.
[2] K. Fujisawa, Y. Noguchi, Y. Miyashita, K. Okamoto, N. Lehnert, Inorg. Chem. 46
(2007) 10607.
[3] H.V.R. Dias, S. Singh, J.A. Flores, Inorg. Chem. 45 (2006) 8859.
[4] H.V.R. Dias, S. Singh, Inorg. Chem. 43 (2004) 5786.
[5] J.K. Voo, K.C. Lam, A.L. Rheingold, C.G. Riordan, J. Chem. Soc., Dalton Trans.
(2001) 1803.
[6] S.M. Carrier, C.E. Ruggiero, W.B. Tolman, J. Am. Chem. Soc. 114 (1992) 4407.
[7] A. Boni, G. Pampaloni, R. Peloso, D. Belletti, C. Graiff, A. Tiripicchio, J.
Organomet. Chem. 691 (2006) 5602.
[8] R.A. Himes, G.Y. Park, A.N. Barry, N.J. Blackburn, K.D. Karlin, J. Am. Chem. Soc.
129 (2007) 5352.
[9] E.A. Lewis, W.B. Tolman, Chem. Rev. 104 (2004) 1047.
[10] L.M. Mirica, X. Ottenwaelder, T.D.P. Stack, Chem. Rev. 104 (2004) 1013.
[11] G. Battaini, M.D. Carolis, E. Monzani, F. Tuczek, L. Casella, Chem. Commun.
(2003) 726.
[12] N.W. Aboelella, E.A. Lewis, A.M. Reynolds, W.W. Brennessel, C.J. Cramer, W.B.
Tolman, J. Am. Chem. Soc. 124 (2002) 10660.
Scheme 4. Fluorescence spectra of ligand LH (black line), complexes 3ꢀClO4 (red
line) and 5 (blue line) in CH2Cl2 excited at 340 nm at room temperature with a
concentration of 5.6 ꢄ 10ꢂ5 M.
system, as follows: kmax = 395 nm, Uf = 0.090 for LH; Uf ꢃ 0.00 for
complex 3ꢀClO4 and kmax = 377 nm, Uf = 0.010 for 4ꢀClO4 (S4);
kmax = 393 nm, Uf = 0.034 for complex 5 in CH2Cl2 when excited
at k = 340 nm. On the whole, the quantum yield for two or three
coordinate copper(I) derivatives is a little different between the ri-
gid and nonrigid states but not prominent, indicating that the
influence of structural rigidity on the quenching effect is minor.
The main reason for significant quenching can be ascribed to the
electronic factor [17].
[13] L.M. Mirica, M. Vance, D.J. Rudd, B. Hedman, K.O. Hodgson, E.I. Solomon, T.D.P.
Stack, J. Am. Chem. Soc. 124 (2002) 9332.
[14] M. Taki, S. Teramae, S. Nagatomo, Y. Tachi, T. Kitagawa, S. Itoh, S. Fukuzumi, J.
Am. Chem. Soc. 124 (2002) 6367.
4. Conclusions
[15] S.M. Carrier, C.E. Ruggiero, R.P. Houser, W.B. Tolman, Inorg. Chem. 32 (1993)
4889.
[16] C.-C. Chou, H.-J. Liu, C.-C. Su, Dalton Trans. (2008) 3358.
[17] C.-C. Chou, H.-J. Liu, L.H.-C. Chao, Chem. Commun. (2009) 6382.
[18] H.-C. Liang, K.D. Karlin, R. Dyson, S. Kaderli, B. Jung, A.D. Zuberbühler, Inorg.
Chem. 39 (2000) 5884.
[19] G.M. Sheldrick, Acta Crystallogr., Sect. A64 (2008) 112.
[20] The van der Walls limit is 2.95 Å for CuI. . .N A. Bondi, J. Phys. Chem. 68 (1964)
441.
[21] T.N. Sorrell, D.L. Jameson, J. Am. Chem. Soc. 105 (1983) 6013.
[22] T.N. Sorrell, M.R. Malachowski, D.L. Jameson, Inorg. Chem. 21 (1982) 3250.
[23] T.N. Sorrell, M.R. Malachowski, Inorg. Chem. 22 (1983) 1883.
[24] S. Schindler, D.J. Szalda, C. Creutz, Inorg. Chem. 31 (1992) 2255.
[25] K.D. Karlin, J.C. Hayes, Y. Gultneh, R.W. Cruse, J.W. McKown, J.P. Hutchinson, J.
Zubieta, J. Am. Chem. Soc. 106 (1984) 2121.
The existence of fluxional behavior in coordinatively unsatu-
rated mononuclear copper(I) complexes has been very rare so far
[16,17]. This study reveals an interesting steric influence of 2-sub-
stituents in the perimidine nucleus on the fluxionality of two and
three coordinate copper(I) complexes. Additionally, it is observed
that the consequent influence of fluxional behavior on fluorescence
quenching is minor for the presented two or three coordinate cop-
per(I) complexes. The electronic perturbation of the perimidine nu-
cleus is the principal cause of alteration of the fluorescence
intensity of these low coordinate copper(I) complexes.
[26] G.A. Bowmaker, G.R. Clark, D.A. Roger, A. Camus, N. Marsich, J. Chem. Soc.,
Dalton Trans. (1984) 37.
Acknowledgements
[27] P.C. Healy, C. Pakawatchai, A.H. White, J. Chem. Soc., Dalton Trans. (1983)
1917.
[28] T.N. Sorrell, A.S. Borovik, Inorg. Chem. 26 (1987) 1957.
Financial support from the National Science Council of the
Republic of China (NSC 98-2113-M-255-001-MY2) is gratefully